1. Field of the Invention
The present invention relates to carbon materials including fullerenes as its components, especially fine carbon wires, and methods for producing the same.
2. Description of the Related Art
C60 is a typical fullerene. It is known that a needle-like substance containing C60 can be obtained from a solution of C60 in toluene (See S. Ogawa, H. Furusawa, T. Watanabe, and H. Yamamoto, “Observation of condensed structure of C60 assembled from solution” Journal of Physics and Chemistry of Solids, 61(2000) 1045-1050).
However, the reference only shows a technique in which C60 is deposited from a solution of C60 in toluene and thereby yields such a needle-like substance. According to this technique, the needle-like substance very slowly grows to about 20 mm in length over six months. The growth rate of the needle-like substance of C60 according to the technique is excessively low and it takes a much long time for the needle-like substance to grow.
According to such conventional techniques, a practically sufficient growth rate cannot be obtained in the production of one-dimensional substances including fullerenes as its components, especially wire-like carbon materials.
The conventional needle-like substance of C60 is obtained by depositing from a solution of C60 containing toluene alone as a solvent. The resulting needle-like substance is amorphous (see the aforementioned reference).
Japanese Unexamined Patent Application Publication No. 10-1306 discloses a cluster obtained by adding a poor solvent for fullerenes to a solution of a fullerene monomer.
Such a cluster, however, is made of the fullerene monomer associated by the van der Waals force and is not a crystal but a granule.
It is also known that the needle-like substance of C60 can also be obtained by evaporating a solution of C60 in a mixture of 95 wt % of hexane and 5 wt % of benzene or a solution having a similar composition at temperatures ranging from room temperature to 80° C. (Y. Yosida, Jpn. J. Appl. Phys. 1992; 31: L505, “Scanning electron microscope images of C60 whiskers”).
The needle-like crystal of the above-mentioned substance has a very rough surface and is apparently different from a needle-like fullerene crystal having a smooth surface. In addition, the scanning electron microscope images of the needle-like crystal in the reference show that this crystal is a polycrystal.
Electric drive mechanisms of microminiature devices such as micro-sensor assemblies and micromachines require fine conductive wires for supplying electricity. However, fine metal wires include grain boundaries formed by crystallization and inevitably cause increased electric resistance due to segregation of dopants into the grain boundaries, and rupture and increased surface roughness at the grain boundaries.
The tip shapes of such fine metal wires depend n the crystal habit of the metal crystals, and the fine metal wires can hardly have a nearly spherical tip having a curvature on the order of nanometers.
In addition, the metallic fine wires cannot significantly have a chemically modified structure by combining a specific functional group to the surface so as to constitute a higher order structure.